1. Field of the Invention
The present invention relates to a drive circuit, and more particularly to a drive circuit outputting a potential corresponding to an input potential to an output node.
2. Description of the Background Art
In a semiconductor integrated circuit device, there has been incorporated a drive circuit for transmitting to a load a potential generated in a potential generating circuit having a small drive capability. FIG. 80 is a circuit diagram showing a configuration of such a drive circuit 300. In FIG. 80, drive circuit 300 includes: P-type field effect transistors (hereinafter, referred to as P-type transistors) 301 and 302; N-type field effect transistors (hereinafter, referred to as N-type transistors)303 and 304; and a constant current source 305.
P-type transistors 301 and 302 are connected between a node of power supply potential VCC and a node N301 and between the node of power supply potential VCC and a node N302, respectively, and the gates thereof are connected both to node N301. P-type transistors 301 and 302 constitute a current mirror circuit. N-type transistor 303 is connected between node N301 and a N305, and the gate thereof is connected to an input node N303. N-type transistor 304 is connected between nodes N302, and N305 and the gate thereof is connected to an output node N304 and node N302. Constant current source 305 is connected between node N305 and a node of ground potential GND to supply a constant current.
A current of a value corresponding to a potential VI at input node N303 flows in N-type transistor 303. Since N-type transistor 303 and P-type transistor 301 are connected in series with each other and P-type transistors 301 and 302 constitute a current mirror circuit, currents of the same value flow through transistors 301 to 303. In a case where a potential VO at output node N304 is lower than an input potential VI, a current flowing in N-type transistor N304 is smaller than that flowing through transistors 301 and 303 to raise output potential VO. In a case where potential VO at output node N304 is higher than input potential VI, a current flowing in N-type transistor N304 is larger than that flowing through transistors 301 and 303 to lower output potential VO. Accordingly, output potential VO becomes equal to input potential VI.
In a conventional drive circuit 300, however, since a constant through-current always flows into the node of ground potential GND from the node of power supply potential VCC through transistors 301 to 304, and constant current source 305, there has been a problem of high current consumption.